共查询到20条相似文献,搜索用时 344 毫秒
1.
2.
Jungang Gao X. Zhang L. Huo H. Zhao 《Journal of Thermal Analysis and Calorimetry》2010,100(1):225-232
The curing kinetics of a bi-component system about o-cresol-formaldehyde epoxy resin (o-CFER) modified by liquid crystalline p-phenylene di[4-(2,3-epoxypropyl) benzoate] (p-PEPB), with 3-methyl-tetrahydrophthalic anhydride (MeTHPA) as a curing agent, were studied by non-isothermal differential
scanning calorimetry (DSC) method. The relationship between apparent activation energy E
a and the conversion α was obtained by the isoconversional method of Ozawa. The reaction molecular mechanism was proposed. The results show that
the values of E
a in the initial stage are higher than other time, and E
a tend to decrease slightly with the reaction processing. There is a phase separation in the cure process with LC phase formation.
These curing reactions can be described by the Šesták–Berggren (S–B) equation, the kinetic equation of cure reaction as follows:
\frac\textda\textdt = Aexp( - \fracE\texta RT )am ( 1 - a )n {\frac{{{\text{d}}\alpha }}{{{\text{d}}t}}} = A\exp \left( { - {\frac{{E_{\text{a}} }}{RT}}} \right)\alpha^{m} \left( {1 - a} \right)^{n} . 相似文献
3.
Le Xin Song Chuan Feng Teng Peng Xu Hai Ming Wang Zi Qiang Zhang Qing Qing Liu 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):223-233
The present work revealed there was a conceptual difference in the thermal decomposition behaviors between the complexed β-cyclodextrin
(CD) in an inclusion system and the β-CD complex of guest. The thermal decomposition behaviors of the solid inclusion complexes
of β-CD with ethylenediamine (Eda), diethylenetriamine (Dta) and triethylamine (Tea) were investigated using nonisothermal
thermogravimetry (TG) analysis based on weight loss as a function of temperature. In view of TG profiles, a consecutive mechanism
describing the formation and thermal decomposition of the three solid supermolecules of β-CD was presented. Heating rate has
very different effects on the thermal decomposition behaviors of these complexes. The faster the heating rate is, the higher
the melting-decomposition point of the complexed β-CD in an inclusion system is, and on the whole the bigger the rate constant
(k) of the thermal decomposition reaction of the complexed β-CD is. The thermal decomposition process of the complexed β-CD
for each inclusion system is determined to be simple first-order reaction using Ozawa method. The apparent activation energies
(E
a) and frequency factors (A) of the thermal decomposition reactions of the complexed β-CD molecules have been also calculated. It is found that when
the decomposition reaction of the complexed β-CD encountered a large value of E
a, such as that in Dta–β-CD system, an apparent compensation effect of A on E
a can provide enough energy to conquer the reaction barrier in prompting the k value of thermal decomposition reaction of the complexed β-CD according to Arrhenius equation. 相似文献
4.
The kinetics of the isothermal adsorption of ethanol from an aqueous solution onto a hydrophobic zeolite of the NaZSM-5 type
in the temperature range 298–333 K was investigated. Specific shape parameters of the adsorption degree curves were determined.
The changes in the specific shape parameters of the adsorption degree curves with temperature were determined. The kinetic
parameters of ethanol adsorption (Ea,ln A) were determined by the initial rate, the saturation rate and the maximum rate methods as well as from the Johnson, Mehl
and Avramy equation. The kinetic model of ethanol adsorption kt=[1−(1−α)1/3] was determined by the “model fitting” method.
Ethanol adsorption from aqueous solution onto NaZSM-5 is a kinetically controlled process limited by the rate of three-dimensional
movement of the boundary layer of the adsorption phase. A model for the mechanism of ethanol adsorption onto NaZSM-5 is suggested
on the basis of the kinetic model. Ethanol molecules in aqueous solution are associated in clusters. The activation energy
of the adsorption process corresponds to the energy required for the detachment of an ethanol molecule from a cluster and
its adsorption onto the zeolite. 相似文献
5.
D. S. Dias M. S. Crespi C. A. Ribeiro J. L. S. Fernandes H. M. G. Cerqueira 《Journal of Thermal Analysis and Calorimetry》2008,91(2):409-412
Samples of paint (P), reused PET (PET-R) and paint/PET-R mixtures (PPET-R) were evaluated using DSC to verify their physical-chemical
properties and thermal behavior. Films from paints and PPET-R are visually similar. It was possible to establish that the
maximum amount of PET-R that can be added to paint without significantly altering its filming properties is 2%. The cure process
(80–203°C) was identified through DSC curves. The kinetic parameters, activation energy (E
a) and Arrhenius parameters (A) for the samples containing 0.5 to 1% of PET-R, were calculated using the Flynn-Wall-Ozawa isoconversional method. It was
observed that for greater amounts of PET-R added, there is a decrease in the E
a values for the cure process. A Kinetic compensation effect (KCE), represented by the equation InA=−2.70+0.31E
a was observed for all the samples. The most suitable kinetic model to describe this cure process is the autocatalytic Šesták-Berggreen,
model applied to heterogeneous systems. 相似文献
6.
Lei Zhang Hongmei Li Xueyan Liu Pingli Kang 《Russian Journal of Inorganic Chemistry》2012,57(4):622-628
Titanium dioxide nanoparticles were employed for the sorption of Ge(IV) ions from aqueous solution. The process was studied
in detail by varying the sorption time, pH, and temperature. The sorption process was found to be fast, equilibrium was reached
within 3 min. A maximum sorption could be achieved from solution when the pH ranges between 4.0 and 11.0. Sorbed Ge(IV) ions
can be completely desorbed with 2 mL of 0.3 mol L−1 K3PO4-1.0 mol L−1 H2SO4 mixture solution. The kinetic experimental data properly correlate with the second-order kinetic model (k
2 = 0.88 g mg−1 min−1 (25°C)), Reichenberg equation and Morris-Weber model. The estimated E
a
for Ge(IV) adsorption on nano-TiO2 was 19.66 kJ mol−1. The overall rate process appears to be influenced by intra-particle diffusion. The sorption data could be well interpreted
with the Langmuir and Dubinin-Radushkevich (D-R) type sorption isotherms. The D-R parameters were calculated to be K = −0.00321 mol2 kJ−2, q
m
= 0.59 mmol g−1 and E = 12.48 kJ mol−1 at room temperature. Furthermore, the thermodynamic parameters were also determined, and the ΔH
0 and ΔG
0 values indicated a spontaneous exothermic behavior. 相似文献
7.
Z. Fengqui H. Rongzu S. Jirong G. Hongxu 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(7):1034-1036
The kinetic parameters of the exothermic decomposition of the title compound in a temperatureprogrammed mode have been studied
by means of DSC. The DSC data obtained are fitted to the integral, differential, and exothermic rate equations by the linear
least-squares, iterative, combined dichotomous, and least-squares methods, respectively. After establishing the most probable
general expression of differential and integral mechanism functions by the logical choice method, the corresponding values
of the apparent activation energy (E
a), preexponential factor (A), and reaction order (n) are obtained by the exothermic rate equation. The results show that the empirical kinetic model function in differential
form and the values of E
a and A of this reaction are (1 − α)−4.08, 149.95 kJ mol−1, and 1014.06 s−1, respectively. With the help of the heating rate and kinetic parameters obtained, the kinetic equation of the exothermic
decomposition of the title compound is proposed. The critical temperature of thermal explosion of the compound is 155.71°C.
The above-mentioned kinetic parameters are quite useful for analyzing and evaluating the stability and thermal explosion rule
of the title compound.
The text was submitted by the authors in English. 相似文献
8.
Non-isothermal kinetics of free-radical polymerization of 2,2-dinitro-1-butyl acrylate 总被引:1,自引:0,他引:1
S. H. Du G. Z. Zhang H. H. Li P. Wang X. C. Wang 《Journal of Thermal Analysis and Calorimetry》2009,95(2):427-431
The free-radical bulk polymerization of 2,2-dinitro-1-butyl-acrylate (DNBA) in the presence of 2,2′-azobisisobutyronitrile
(AIBN) as the initiator was investigated by DSC in the non-isothermal mode. Kissinger and Ozawa methods were applied to determine
the activation energy (E
a) and the reaction order of free-radical polymerization. The results showed that the temperature of exothermic polymerization
peaks increased with increasing the heating rate. The reaction order of non-isothermal polymerization of DNBA in the presence
of AIBN is approximately 1. The average activation energy (92.91±1.88 kJ mol −1) obtained was smaller slightly than the value of E
a=96.82 kJ mol−1 found with the Barrett method. 相似文献
9.
10.
Hadi Kalali Friedrich Kohler Peter Svejda 《Monatshefte für Chemie / Chemical Monthly》1987,118(1):1-18
The excess properties of the mixture bis(2-dichloroethyl)ether (chlorex) + 2,2,4-trimethylpentane (isooctane), i.e. excess volumev
E, excess enthalpyh
E, excessGibbs energyg
E and excess heat capacityc
p
E
are reported. The excess volume is small, negative on the chlorex side and positive on the isooctane side. The excess enthalpy at 293.15 K is 1 913 J mol–1 for equimolar composition, the excessGibbs energy amounts to 1 367 J mol–1 under the same conditions. The system undergoes phase separation below 290.47 K. Due to the nearness of the critical point,c
p
E
exhibits a strong maximum at the critical composition (x
isooctane=0.508), though the basic part ofc
p
E
is negative. Discussion focusses on the effects of polarity of chlorex as mixing partner, on near-critical properties, and on mixing rules of avan der Waals-type equation of state.Dedicated to Prof. Dr.K. Komarek on the occasion of his 60th birthday. 相似文献
11.
Studies on direct-current electrical conductivity and optical properties of a new solution of processable conducting polymer
are reported. Electrical conductivity of thin films of the polymer on glass plate at room temperature was 6×10−6 S/cm. Study of conductivity with variation of temperature does not provide any definite thermal activation energy, which
is in accordance with the amorphous nature of polymer. Optical absorption data adopting the Bardeen equation showed that maximum
‘optical gap’ (E
g
) is 3.30 eV. Doping with Br2-vapor was found to be only partially effective in decreasingE
g
by 0.43 eV. The polymer was found to be quite stable under normal atmospheric conditions. Environmental stability of both
undoped and doped polymer has been discussed.
Part 2: [5] 相似文献
12.
Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric
(TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of
ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method
of Vyazovkin were used to investigate the dependence of activation energy (E
a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived
from isothermal data. A strong dependence of E
a with α is observed for the ADN prills. All the methods showed an initial increase in E
a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E
a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E
a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol−1, respectively. 相似文献
13.
The electropolymerisation of N-benzylaniline (NBA) at transparent ITO glass electrodes was investigated with in situ UV-visible spectroelectrochemistry.
An intermediate was found to be generated during electrolysis as the precursor of poly(N-benzylaniline) (PNBA). The intermediate, which shows an absorbance band at λ = 460 nm, is able to react spontaneously with
NBA, forming a polymeric end product, which is deposited on the electrode surface. UV-Vis spectra were obtained with PNBA-modified
electrodes at various electrode potentials. It was shown that the colouration of the PNBA film after a positive-going potential
step proceeds ca. 5 times slower than its discolouration after the reverse negative-going potential step. Anodic degradation
of PNBA film was shown to proceed when holding the electrode at a sufficiently high positive potential. A linear dependence
between the first-order degradation rate constant (k/s−1) and electrode potential (E/V) was found in the potential range of E
RHE = +0.8 to +1.1 V: log k = a + bE, where a = −8.75 and b = 5.45 are empirical coefficients. In the whole spectral range investigated, the degradation of PNBA was found to proceed
faster as compared to that of polyaniline (for polyaniline, coefficients a = −12.7 and b = 8.96 were obtained in the potential range of E
RHE = +0.85 to +1.1 V). The electrooxidation of hydroquinone, as well as the electroreduction of benzoquinone, were shown to
proceed at PNBA-modified electrodes. In these processes, PNBA was shown to play the role of an electron mediator between the
ITO electrode and solution phase redox species.
Received: 8 January 1999 / Accepted: 27 January 1999 相似文献
14.
B. V. L’vov 《Journal of Thermal Analysis and Calorimetry》2006,84(3):581-587
The main purpose of this
paper is to prove the applicability of the mechanism of congruent dissociative
vaporization (CDV) to the solid-state decomposition kinetics through the comparison
of the fundamental theoretical relationship Ei/Ee=(a+b)/a resulted
from this mechanism with experiment. It has been shown that the ratios of Ei and Ee
parameters of the Arrhenius equation measured in the isobaric and equimolar
modes (in the presence and absence of H2O vapour) for
22 reactants with the general formula aSalt⋅bH2O or aOxide⋅bH2O are in agreement with
the values of (a+b)/a. The relative standard deviation is only 17% and
the correlation coefficient is close to 0.99. A probability of accidental
correlation for all set of the E parameters
taken from the literature is lower than 4⋅10–16
. This strongly supports the validity of the CDV mechanism. The problem of
stability of polyatomic molecules of inorganic salts in the gaseous state,
which are the primary decomposition products of crystalline hydrates, was
also discussed on the basis of recent mass spectroscopy studies. It was concluded
that any doubts in the applicability of the CDV mechanism as a general mechanism
of solid-state decomposition reactions are unsound. 相似文献
15.
Densities (ρ), viscosities (η) and speeds of sound (u) of the ternary mixture (1-heptanol + tetrachloroethylene + methylcyclohexane) and the corresponding binary mixtures (1-heptanol + tetrachloroethylene),
(1-heptanol + methylcyclohexane) and (tetrachloroethylene + methylcyclohexane) at 298.15 K were measured over the whole composition
range. The data obtained are used to calculate the excess molar volumes (V
E), excess isobaric thermal expansivities (α
E), viscosity deviations (Δη), excess Gibbs energies of activation of viscous flow (ΔG
*E) and excess isentropic compressibilities (κ
S
E) of the binary and ternary mixtures. The data from the binary systems were fitted by the Redlich–Kister equation whereas
the best correlation method for the ternary system was found using the Nagata equation. Viscosities, speeds of sound and isentropic
compressibilities of the binary and ternary mixtures have been correlated by means of several empirical and semi-empirical
equations. The best correlation method for viscosities of binary systems is found using the Iulan et al. equation and for
the ternary system using the Heric and McAllister equations. The best correlation method for the speeds of sound and isentropic
compressibilities of the binary system (1-heptanol + methylcyclohexane) is found using IMR (Van Deal ideal mixing relation)
and for the binary system (tetrachloroethylene + methylcyclohexane) it is found using the NR (Nomoto relation) and for the
binary system (1-heptanol + tetrachloroethylene) and the ternary system (1-heptanol + trichloroethylene + methylcyclohexane)
it is obtained from the FLT (Jacobson free length theory). 相似文献
16.
A critical analysis of the use of an overall single rate reaction equation instead of the true rate equation corresponding
to a complex process consisting in two consecutive reactions is presented. In accordance with this approximation, often used
in the kinetic analysis of the system in which several reactions take place, the overall process is described by the apparent
activation parameters (the apparent activation energy, E
ap, and the apparent pre-exponential factor, A
ap) and the apparent conversion function.
The theoretical isotherms (α=α(t), where a is the conversion degree and t is the time) have been simulated for a system in which two consecutive reactions occur. In this case, the apparent activation
parameters depends on: (a) the considered range of the temperature; (b) the temperature, for a given conversion degree. It
is shown that the apparent activation parameters are corrrelated by the compensation effect relationship: lnA
ap=α*+β*E
ap where α* and β* are the parameters of the linear regression.
The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those
for which these parameters were evaluated, is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Excess Molar Volume and Viscosity of Isobutyric Acid + Water Binary Mixtures Near and Far Away from the Critical Temperature 总被引:1,自引:0,他引:1
The excess molar volume VE, shear viscosity deviation Δη and excess Gibbs energy of activation ΔG∗E of viscous flow have been investigated by using density (ρ) and shear viscosity (η) measurements for isobutyric acid + water (IBA+W) mixtures over the entire range of mole fractions at five different temperatures,
both near and close to the critical temperature (2.055K ≤ (T−Tc)≤ 13.055K). The results were also fitted with the Redlich–Kister equation. This system exhibited very large negative values
of VE and very large positive values of Δη due to increased hydrogen bonding interactions and correlation length between unlike molecules in the critical region and
to very large differences between the molar volumes of the pure components at low temperatures. The activation parameters
ΔH∗ and ΔS∗ have been also calculated and show that the critical region has an important effect on the volumetric properties. 相似文献
18.
G. Vázquez J. González-Álvarez G. Antorrena 《Journal of Thermal Analysis and Calorimetry》2006,84(3):651-654
The
curing of a phenol–formaldehyde–tannin (PFT) adhesive in the presence
of pine or eucalyptus wood has been studied using differential scanning calorimetry.
The influence of the adhesive/wood ratio on the activation energy (Ea), the temperature of the
maximum of the exothermic peak (Tp)
and the enthalpy of the curing process (ΔH)
was analysed. Ea, Tp and ΔH
of the curing reaction decreased when wood was added in the curing system.
The adhesive/wood interaction did not depend significantly on wood species. 相似文献
19.
Measurements of the electrophoretic mobility (u
E) of particles of colloidal α-alumina were made as a function of pH, electrolyte concentration and electrolyte type (NaCl,
NaNO3 and KCl) using two similar instrumental techniques. Significant differences (50% or less) in the values of u
E of particles in NaCl were obtained from the two instruments; however, the isoelectric points (IEPs) (the pH at which u
E=0), estimated from the two sets of measurements, occurred at 7.5 ± 0.3 and 7.8 ± 0.05 and were not significantly different.
The latter estimate corresponds with those for particles in KCl and NaNO3 of 8.05 ± 0.11 and 7.95 ± 0.18, respectively, made using the same instrument and indicate that the IEP was a weak function
of electrolyte type. When cations acted as counterions (pH > IEP), the absolute magnitudes and the ranges of u
E with electrolyte concentration were found to be significantly less than when anions acted as counterions (IEP > pH). Estimates
of the zeta potential (ζ), made using various procedures, showed variations of up to 25% at low ratios of electrical-double-layer
thickness (κ
−1) to particle radius (a) (κa∼10) and were of a similar scale to differences in u
E, but no significant variations (95% confidence) in ζ were obtained at high values (κa∼200).
Received: 12 July 2000 Accepted: 17 October 2000 相似文献
20.
The cure behavior, thermal stability, and mechanical properties of diglycidylether of bisphenol A (DGEBA)/polysulfone (PSF) blends initiated by 1 wt % N‐benzylpyrazinium hexafluoroantimonate as a cationic latent catalyst were investigated. The DGEBA/PSF content was varied within 100/0–100/40 wt %. Latent properties were studied through the measurement of the conversion as a function of the curing temperature, and the cure activation energy (Ea) was studied by the Kissinger method with a dynamic differential scanning calorimetry analysis. The thermal stabilities, largely based on the integral procedural decomposition temperature (IPDT) and decomposed activation energy (Et), were investigated by the measurement of thermogravimetric analysis. For the mechanical properties of the casting specimens, the critical stress intensity factor (KIC) test was performed, and their fractured surfaces were examined with scanning electron microscopy. Ea, IPDT, Et, and KIC increased with PSF increasing in the neat epoxy resin up to 30 wt %. However, there was a marginal decrease in the blend system in both the thermal and mechanical properties due to the phase separation between DGEBA and PSF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 121–128, 2001 相似文献